The fast charging capability of battery electric vehicles is seen as a key enabler for a convenient e-mobility and a broad customer acceptance. However, this is a remaining challenge in the development of battery systems. Fast charging results in increased heat losses in the battery cells and the electrical connectors of a battery module. Consequently, battery thermal management plays a crucial role to keep the battery temperature in the recommended range and as homogeneous as possible to avoid accelerated degradation of the cells. In this regard, it is eminently important to understand how thermal management concepts can influence the battery performance in detail.

In this contribution, the combination of numerical simulations and corresponding experiments is used to perform an in-depth analysis of the impact of different thermal management concepts on battery behavior. Battery modules equipped with automotive NMC/Si-Gr pouch cells in application-related setups were explicitly developed for this study (Fig 1). The concept of immersion cooling and bottom cooling, as well as variations of each of those concepts are investigated and compared under various boundary conditions. For the first time, a novel and specifically developed coupled simulation of the respective battery modules is used to extend the findings of the experimental measurements by correlating boundary conditions on module scale to resulting local conditions inside the cells.

With the novel modelling approach, the interactions of electrochemical, electrical, thermal and fluid dynamic phenomena during fast charging are revealed and compared for different thermal management concepts. The approach combines capabilities of small-scale electrochemical models and 3D CFD simulations (Fig. 2). Critical conditions during fast charging such as temperature hot spots and areas of negative anode potential are identified and discussed regarding long-term degradation. Emerging inhomogeneities in current density, SOC and temperature and their effect on the battery performance during operation are analyzed on cell and module level (Fig 3).

While the long-term degradation is investigated with the experimental modules, optimized thermal management solutions for increased performance during fast charging are derived and presented using the numerical models. It will be illustrated how innovative thermal management solutions can be used to diminish hot spots, increase the temperature homogeneity in the cells, and at the same time avoid lithium plating during fast charging.